When controlling a rotating device, for example a motor, rotation information should be detected precisely and rapidly. When controlling a rotating device, a movement or rotating location of a rotating body should be measured accurately by means of a rotation angle detecting device installed at a rotary shaft. A resolver and an encoder have been adopted and used for such measurement, and these detecting devices have advantages and disadvantages. The resolver directly detects an absolute location of a rotor and calculates a rotating direction and a rotating speed by means of the change of location of the rotor.
An electric power steering (EPS) is used for a vehicle in order to assist the operation of a handle by driving a motor with a battery. The electric power steering receives attention as an efficient system with a less power loss of an engine, in comparison to a case where a hydraulic pressure is generated by means of a rotating force of an engine. Since the EPS needs precise control, a rotation angle detecting device for precisely detecting a rotation angle of the motor is required, and the rotation angle detecting device demands high reliability. As such a rotation angle detecting device for a vehicle, a resolver having higher environment resistance in comparison to an encoder is used.
The resolver is a kind of sensor for precisely measuring a rotating speed and a rotation angle of a motor. Generally, the resolver has a relatively simple structure in which both an excitation coil and an output coil are located at a stator and an oval or multi-pole rotor is located at an inner side of the stator. A resolver having this structure is disclosed in Japanese Unexamined Patent Publication No. 1996-178610.
FIG. 1 is a diagram in the above Japanese Unexamined Patent Publication, and a resolver includes a rotor 10 having a rotary shaft provided therethrough and a ring-shaped stator 11 configured to face the rotor 10 with a gap. The rotor 10 has a plurality of salient poles 10a formed along an outer circumference thereof, and the ring-shaped stator 11 has a plurality of teeth 11b and a plurality of slots 11a alternately formed along an inner circumference thereof. In addition, an excitation coil and an output coil are wound on the teeth 11b of the stator 11, and the excitation coil and the output coil are accommodated in the slots 11a. Here, the output coil is composed of a first output coil and a second output coil. If an excitation power is applied to the excitation coil and the rotary shaft is rotated, a sine signal and a cosine signal are output from the first output coil and the second output coil, and a rotation angle of the resolver may be known by analyzing the signals.
As described above, in the resolver, the coils wound on the teeth 11b of the stator 11 is an important element for inputting and outputting signals, and thus a precise design is demanded when winding the coils at a rotation angle detecting device such as a resolver. For example, if a coil is wound more on the teeth 11b, an area occupied by the coil at the slot 11a between the teeth 11b increases, which causes electric interference between coils wound on two adjacent teeth 11b and results in an error. If a coil is wound less on the teeth 11b, a transformation ratio of an induced voltage of the output coil is lowered, which becomes vulnerable to external noise.